This invention relates generally to medical devices or surgical implants such as artificial hip joints and, more particularly to a method and system for smoothing surgical implants such as artificial hip joints using gas cluster ion beam technology.
Total hip replacement, or arthroplasty, is a surgical procedure in which the diseased parts of a hip joint are removed and replaced with new, artificial parts. Presently, these artificial hip joint components are being produced from improved bearing materials such as highly cross-linked polyethylene, metal-on-metal, and ceramic-on-ceramic implants. After the hip replacement, osteolysis is a major problem and is believed to be due to an inflammatory process brought on by particulate matter or debris dislodged from the implants themselves. Some degree of osteolysis is present in up to 40% of all cases within 10 years of surgery.
The problem is articulating surfaces between the femoral and acetabular components of the implant produce wear debris which is an important contributor to pathologic tissue response. Therefore, the long-term threat to component failure from a biologic standpoint is this wearing debris associated with osteolysis. The critical initiating sequence involves the interaction between small particulate materials and responding specialized cells. The number, size, distribution, and type of particulate material are also believed to have an affect on the process.
Quantitatively, the material causing the most tissue reaction appears to be the particulate polyethylene with particle sizes of approximately 0.5 micron. Metallic debris also causes tissue reaction with significant quantities identified with particle sizes somewhat larger than the polyethylene debris. The major effect of this larger metallic debris may relate to promoting wear of the polyethylene, with the derivative polyethylene particles of submicron size triggering the cellular response. However, smaller metal particles and ions have been demonstrated to be active in direct stimulation of biologic processes as well.
It is therefore an object of this invention to provide an atomic level surface smoothing of artificial hip joints.
It is a further object of this invention to provide surface modification of artificial hip joints by gas cluster ion beams to alleviate the problems associated with osteolysis.
The objects set forth above as well as further and other objects and advantages of the present invention are achieved by the invention described hereinbelow.
Several factors have been suggested to minimize the production of wear debris: (1) femoral heads with highly polished cobalt alloy or polished ceramics are believed to be advantageous in minimizing effects of wear on the polyethylene surfaces of the acetabular cups; (2) new highly cross-linked polyethylene acetabular cups are gaining some increased surgical use as a means of decreasing wear and; (3) hard-on-hard implants such as metal-on-metal and ceramic-on-ceramic implants are expected to reduce wear debris.
Regardless of the materials used in the artificial hip joint designs, the present invention applies gas cluster ion beam (GCIB) technology in order to modify the component""s surface, thereby substantially reducing wear debris and osteolysis complications. The approach of the surface modification comprises an atomic level surface smoothing utilizing GCIB to super smooth the femoral heads and/or the surfaces of the acetabular cups to reduce frictional wear at the interface of the bearing surfaces.
A reduction in polyethylene debris and metal debris by GCIB smoothing on one or both bearing surfaces of a total hip prosthesis reduces osteolysis, results in a substantial cost savings to the healthcare system, and reduces patient pain and suffering.
For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims.